Cable television systems typically include a headend section for receiving satellite signals and demodulating the signals to baseband. The baseband signal is then converted to an optical signal for transmission from the headend section over fiber optic cable. Optical transmitters are distributed throughout the cable system for splitting and transmitting optical signals, and optical receivers are provided for receiving the optical signals and converting them to radio frequency (RF) signals that are further transmitted along branches of the system over coaxial cable rather than fiber optic cable. Taps are situated along the coaxial cable to tap off the cable signals to subscribers of the system.
Various factors influence the ability to accurately transmit and receive optical signals within a cable television system. For example, temperature fluctuations in the laser environment and the laser itself, which cause variations in the optical modulation index of the optical transmitter, can result in variations in the output power of the laser in the optical transmitter and corresponding variations in the radio frequency (RF) output level of the optical receiver. These temperature variations, which can result in incorrect decoding and processing of the optical signal, can be significant in uncooled lasers, since the heat generated by the laser diode itself contributes to environmental temperature fluctuations.
Thus, what is needed is a better way to provide temperature-independent transmission of optical signals within a cable television system.